Wednesday, December 25, 2013

6AS7 headphone amp with Sophia Mesh Plate 274B rec. tube

The power supply and amp section are on two die-cast Al bases. A Sophia Mesh Plate Princess 274B rec. tube does the rectification. The PS has its own power filter to reduce EMI\RFI and the mains cable is choked. The power tranni is Hammond and the 20H choke is Hammond also and these are both isolated from the chassis by rubber grommets to control vibration. The 6AS7 power tube is NOS Winged "C" Svetlana and a NOS Tesla E88CC gold pin for the driver and is directly coupled. XLRs connect the HT and AC filament current to the amp section. A single 6.5mm input upfront with dual headphone output. Attenuation is provided by an Alps Blue Velvet pot. Both enclosures are dampened with bitumanised Al foil and the paint is Epoxy Enamel. The attenuator knob is 4 ounces of solid brass.

The Sophia Mesh Plate 274B rec. tube and a 4uf PIO Russian  filter cap start the filtering network with seven stages of filtering and storage in all. I believe the great sound of this amp is due to the Sophia tube and the PIO cap. There is no PCBs or shielded wire used in this amp to dull the sound. Wiring is all point-2-point and component-2-componet. Fine silver plated wire warp wire carries all the audio. The only caps in the amp are the output caps. All PS caps are snubbed with polypropylene caps and the output caps with Russian PIO caps.WBT silver solder is used throughout.

The amp is is absolutely dead quiet. Through my Audio-Technica ATH700 Air headphones music is like I have never heard before. Harmonics are rich and deep, detail is fine grained and dynamics unlimited.This may well be the greatest piece of audio gear I have ever made.

Saturday, December 7, 2013

Inexpensive MM\MC phono preamp MKII

For a 1000th the price of some SS phono preamps on the market these days I'm very happy with the second Bruce (of Oddwatt's fame) deisgn named "Mimic" This can be built in an afternoon and even with batteries cost about $40. Mine runs on 3 X 9V batteries wich should give 50 to 100 hours play with no change. The sound stage is detailed and expansive and instruments have there own place. Over-all tone is flat and natural.

Some better caps were used in this build over the earlier one. WBT silver solder, a dampened enclosure (bitumanised with Al foil)  and wire wrap wire hookup used throughout. A simple off-the-shelf enclosure keeps this preamp cheap. But sound is rich.